The US indexes spent the day Monday in selloff mode. The pundits have offered an array of explanations: weak Chinese GDP, the swan-dive in gold and other commodities, the terrorism in Boston, etc.
The selloff began at the open, and my best-guess regression through a 5-minute chart of the S&P 500 suggests that the selling was relatively consistent through the day. A failed afternoon rally may have been hampered by the Boston tragedy, but the late afternoon trend didn't appear to deviate from the prior trajectory. The index closed eight basis points off its intraday low for a loss of 2.30%. That's the worst decline since the November 7, 2012 post-election rout.
Here is a 5-minute look at yesterday's action.
A daily chart shows that yesterday's selling was on high volume. Unlike that negative volume spike in March, yesterday was not a triple witching day (at least not in the options sense).
The S&P 500 is now up 8.85% for 2013 and 2.57% below the all-time closing high of April 11th.
For a better sense of how these declines figure into a larger historical context, here's a long-term view of secular bull and bear markets in the S&P Composite since 1871.